In fields such as communications, for example, signals are amplified by amplifiers, and distortion generated by amplifiers in the course of amplifying signals is compensated for.
Specifically, amplification apparatuses equipped with a distortion detection loop and a distortion removal loop that use the feedforward method to perform distortion compensation, and amplification apparatuses equipped with a predistorter that use the predistortion method to perform distortion compensation, are being studied. Also being studied is the use of pilot signals constituting reference signals to perform control relating to distortion compensation.
An example of the prior technology will now be described.
In the past, in a feedforward type distortion compensation amplifier equipped with a distortion detection loop and a distortion removal loop, the level of a pilot signal was adjusted based on the level of a signal corresponding to an input signal (see, for example, Patent Document 1).
In the past, in a power amplifier having feedforward type distortion compensation functions, control was effected so that there was always a signal constituting the reference for distortion compensation (see, for example, Patent Document 2).
In the past, when a pilot signal frequency has been set to a first frequency outside the band in a feedforward type common amplifier, based on the frequency dependency of the amount of distortion suppression, the pilot signal frequency was reset to a second frequency within the band so that the level of the pilot signal did not exceed a level at which it would become spurious within the band (see, for example, Patent Document 3).
Patent Document 1
Unexamined Patent Publication No. 2002-76786.
Patent Document 2
Unexamined Patent Publication No. 2002-185267.
Patent Document 3
Unexamined Patent Publication No. 2002-176320.
Patent Document 4
Unexamined Patent Publication No. 2002-76783.
However, the conventional amplification apparatus with distortion compensation capability (distortion compensation amplification apparatus) was still lacking with respect to the configuration for controlling the distortion compensation using a reference signal, so there was a need for further development.
The present invention was accomplished in light of these conventional circumstances, and has as its object to provide, in a configuration that compensates for distortion generated in an amplifier equipped with a distortion detection loop and a distortion removal loop, an amplification apparatus that can improve efficiency with respect to a configuration for control relating to distortion compensation using a reference signal.